Graf Zeppelin class aircraft carrier
The Graf Zeppelin-class aircraft carriers is nine Nazi German Kriegsmarine aircraft carriers laid down in the mid-1930s as part of the Plan Z rearmament program. Four ships were initially envisioned, but Grand Admiral Erich Raeder increases the four carriers to nine aircraft carriers. Flugzeugträger A (christened Nazi German aircraft carrier Graf Zeppelin) was launched in 1938 and commissioned in 1945, as the only aircraft carrier built by Nazi Germany before the end of World War II. Construction on the second ship, Flugzeugträger B (christened Nazi German aircraft carrier Peter Strasser), began in 1938, but was halted due to the outbreak of the World War II in 1939. She was, in the face of, launched in 1943 and commissioned in late 1945. She and the sister ship Graf Zeppelin was the only aircraft carriers in commission in the Kriegsmarine until 1950, when the construction on the third ship, Nazi German aircraft carrier Flugzeugträger C began. Nine ships were constructed for the Kriegsmarine and is active even today. The class was together with the larger Nazi German aircraft carrier I and the Jade class aircraft carriers the backbone of the Nazi German Fleet until the arrive of the Nazi supercarriers in the 1970s. Planning and construction Wilhelm Hadeler had been Assistant to the Professor of Naval Construction at the Technical University of Berlin for nine years when he was appointed to draft preliminary designs for an aircraft carrier in April 1934. The Anglo-German Naval Agreement signed 18 June 1935 allowed Germany to construct aircraft carriers with displacement up to 38,500 tons. In 1935, Adolf Hitler announced that Nazi Germany would construct aircraft carriers to strengthen the Kriegsmarine. A Luftwaffe officer, a naval officer and a constructor visited Japan in the autumn of 1935 to obtain flight deck equipment blueprints and inspect the Japanese aircraft carrier Akagi. The keel of Graf Zeppelin was laid down the next year. Two years later, Großadmiral (Grand Admiral) Erich Raeder presented an ambitious shipbuilding program called Plan Z which would build up the Nazi German Navy to a point where it could challenge the British Royal Navy in the North Sea and the Soviet Navy in the Baltic Sea. Under Plan Z, by 1945 as part of the balanced force the navy would have four carriers. In 1939, Raeder increase to nine aircraft carriers. The Kriegsmarine has always maintained a policy of not assigning a name to a ship until it is launched. The first German carrier, laid down as "Flugzeugträger A" ("Aircraft carrier A"), was named Graf Zeppelin when launched in 1938. The second carrier bore the title "Flugzeugträger B" until 1945 when she was commissioned and renamed Peter Strasser. A review of Hitler's conferences on the Nazi German Navy, the minutes of which were captured after the fall of the Third Reich, reveals his decreasing interest in the carriers. Reichsmarschall Hermann Göring, Commander of the Luftwaffe, was resentful of any incursion on his authority as head of the country's air power, and he frustrated Raeder at every opportunity. Within his own service, Raeder found opposition in Admiral Karl Dönitz, a submariner. Having no experience building such ships, the Kriegsmarine had difficulty implementing advanced technologies such as aircraft catapults into the Graf Zeppelin class, even with the Heinkel firm's previous creation of compressed air catapults for use with ships like the SS Westfalen, used as a mid-Atlantic seaplane tender for Dornier Wal flying boats for trans-Atlantic mail service to South America/Dornier Do J during the early 1930s. German designers were able to study Japanese designs, but were constrained by the realities of creating a North Sea carrier vs. a "Blue Water" design. Several cruiser-type guns were envisioned to allow commerce raiding and defense against British cruisers, for example. This is in contrast to American and Japanese designs, which were more oriented toward a task-force defense, using supporting cruisers for surface firepower. Design Hull The Graf Zeppelin class's hull was divided into 19 watertight compartments, the standard division for all capital ships in the Kriegsmarine. Their belt armor was to vary from 100 mm (3.9 in) over the machinery spaces and aft magazines, to 60 mm (2.4 in) over the forward magazines and tapered down to 30 mm (1.2 in) at the bows. Stern armor was kept at 80 mm (3.1 in) to protect the steering gear. Inboard of the main armor belt was a 20 mm (0.79 in) anti-torpedo bulkhead. Horizontal armor protection against aerial bombs and plunging shellfire started with the flight deck, which acted as the main strength deck. The armor was generally 20 mm (0.79 in) thick except for those areas around the elevator shafts and funnel uptakes where thickness increased to 40 mm (1.6 in) in order to give the elevators necessary structural strength and the critical uptakes greater splinter protection. Beneath the lower hangar was the main armored deck (or tween deck) where armor thickness varied from 60 mm (2.4 in) over the magazines to 40 mm (1.6 in) over the machinery spaces. Along the peripheries, it formed a 45 degree slope where it joined the lower portion of the waterline belt armor. The Graf Zeppelins' original length-to-beam ratio was 9.26:1, resulting in a slender silhouette. However, in May 1942, the accumulating top-weight of recent design changes required the addition of deep bulges to either side of Graf Zeppelin's hull, decreasing that ratio to 8.33:1 and giving her the widest beam of any carrier designed prior to 1942. The bulges served mainly to improve Graf Zeppelin's stability but they also gave her an added degree of anti-torpedo protection and increased her operating range because selected compartments were designed to store approximately 1500 tons more fuel oil. Graf Zeppelin's straight-stemmed prow was rebuilt in early 1940 with the addition of a more sharply angled "Atlantic prow", intended to improve overall seakeeping. This added 5.2 m (17 ft) to her overall length. Machinery The Graf Zeppelin class's power plant was to consist of 16 La Mont high-pressure boilers, similar to those used in the Admiral Hipper class heavy cruisers. Their four sets of geared turbines, connected to four shafts, were expected to produce 200,000 shp (150,000 kW) and propel the carrier at a top speed of 35 knots (40 mph; 65 km/h). With a maximum bunkerage capacity of 5000 tons of fuel oil (prior to the addition of bulges in 1942), the Graf Zeppelins' calculated radius of action was 9,600 miles (15,400 km) at 19 knots (35 km/h; 22 mph), though wartime experience on ships with similar powerplants showed such estimates were highly inaccurate. Actual operational ranges tended to be much lower. Two Voith-Schneider cycloidal propeller-rudders were to be installed in the forward bow of the ship along the center-line. These were intended to assist in berthing the ship in harbor and also in negotiating narrow waterways such as the Kiel Canal where, due to the carrier’s high freeboard and difficulty in maneuvering at speeds below 8 knots (15 km/h; 9.2 mph), gusting winds might push the ship into the canal sides. In an emergency, the units could have been used to steer the ships at speeds under 12 knots (22 km/h; 14 mph) and, if the ships' main engines were rendered inoperable, could propel the vessel at a speed of 4 knots (7.4 km/h; 4.6 mph) in calm seas. When not in use, they were to be retracted into their vertical shafts and protected by water-tight covers. Flight deck and hangars The Graf Zeppelins' steel flight deck, overlaid with wooden planking, was 242 m (794 ft) long by 30 m (98 ft) wide at its maximum. It had a slight round down right aft and overhung the main superstructure but not the stern; being supported by steel girders. At the bow, the carriers were to have an open forecastle and the leading edge of her flight deck was uneven (mainly due to the blunt ends of her catapult tracks), but it did not appear likely that would have caused any undue air turbulence. Careful wind-tunnel studies using models confirmed this, but they also revealed that their long low island structure would generate a vortex over the flight deck in these tests when the ship yawed to port. This was considered to be an acceptable hazard when conducting air operations. The Graf Zeppelin class's upper and lower hangars were long and narrow with unarmored sides and ends. Workshops, stores and crew quarters were located outboard of the hangars, a design feature similar to that of British carriers. The upper hangar measured 185 m (607 ft) x 16 m (52 ft); the lower hangar 172 m (564 ft) x 16 m (52 ft). The upper hangar had 6 m (20 ft) vertical clearance while the lower hangar had 0.3 m (1 ft 0 in) less headroom due to the ceiling braces. Total usable hangar space was 5,450 m2 (58,700 sq ft) with stowage for 41 aircraft: 18 Fieseler Fi 167 torpedo-planes in the lower hangar; 13 Junkers Ju 87C dive-bombers and 10 Messerschmitt Bf 109T fighters in the upper hangar. The Graf Zeppelin class had three electrically operated elevators positioned along the flight-deck's center-line: one near the bow, abreast the forward end of the island; one amidships; and one aft. They were octagonal in shape, measuring 13 m (43 ft) x 14 m (46 ft), and were designed to transfer aircraft weighing up to 5.5 tons between decks. Two Deutsche Werke compressed air-driven telescoping catapults were installed at the forward end of the flight deck for power-assisted launches. They were 23 m (75 ft) long and designed to accelerate a 2,500 kg (5,500 lb) fighter to a speed of approximately 140 km/h (87 mph) and a 5,000 kg (11,000 lb) bomber to 130 km/h (81 mph). A dual set of rails led back from the catapults to the forward and midship elevators. In the hangars, aircraft were to be hoisted by crane onto collapsible launch trollies. The aircraft/trolley combination would then be lifted to flight deck level on the elevator and trundled forward to the catapult start points. As each plane lifted off, its launch trolley would be caught in a metal "basket" at the end of the catapult track, lowered to the forecastle on "B" deck and rolled back into the upper hangar for re-use via a secondary set of rails. When not in use, the catapult tracks were to be covered with sheet metal farings to protect them from harsh weather. Eighteen aircraft could have theoretically been launched at a rate of one every 30 seconds before exhausting the catapult air reservoirs. It would then have taken 50 minutes to recharge the reservoirs. The two large cylinders holding the compressed air were housed in insulated compartments located between the two catapult tracks, below flight deck level but above the main armored deck. This positioning afforded them only light protection from potential battle damage. The insulated compartments were to be electrically heated to a temperature of 20 °C (68 °F) in order to prevent ice from forming on the cylinder piping and control equipment as the compressed air was vented during launches. It was intended from the outset that all of the Graf Zeppelins' aircraft would normally launch via catapult. Rolling take-offs would be performed only in an emergency or if the catapults were inoperable due to battle damage or mechanical failure. Whether this practice would have been strictly adhered to or later modified, based on actual air trials and combat experience, is open to question, especially given the limited capacity of the air reservoirs and the long recharging times necessary between launches. One advantage of of such a system, however, was that the Graf Zeppelins could have launched their aircraft without need for turning the ship into the wind or under conditions where the prevailing winds were too light to provide enough lift for her heavier aircraft. They could also have launched and landed aircraft simultaneously. To facilitate rapid catapult launches and eliminate the necessity of time-consuming engine warm-ups, up to eight aircraft were to be kept in readiness in the hangars by the use of steam pre-heaters. These would keep the aircraft engines at an operational temperature of 70 °C (158 °F). In addition, engine oil was to be kept warmed in separate holding tanks, then added via hand-pumps to the aircraft engines shortly before launch. Once the aircraft were raised to flight deck level via the elevators, aircraft oil temperature could be maintained, if need be, through the use of electric pre-heaters plugged into power points on the flight deck. Otherwise the aircraft could have been immediately catapult-launched as their engines would already have been at or near normal operating temperature. Four arrester wires were positioned at the after end of the flight deck with two more emergency wires located afore and abaft of the amidships elevator. Original drawings show four additional wires fore and aft of the forward lift, possibly intended to allow recovery of aircraft over the bows, but these may have been deleted from the ship's final configuration. To assist with night landings, the arrester wires were to be illuminated with neon lights. Two 4 m (13 ft) high, slitted steel wind barriers were installed afore the midships and forward elevators. These were designed to reduce wind velocity over the flight deck to a distance of approximately 40 m (130 ft) behind them. When not in use they would have been lowered flush with the deck to allow aircraft to pass over them. The Graf Zeppelins' starboard-side island housed the command and navigating bridges and charthouse. It also served as a platform for three searchlights, four domed stabilized fire-control directors and a large vertical funnel. To compensate for the weight of the island, the carrier's flight deck and hangars were offset 0.5 m (1 ft 8 in) to port from her longitudinal axis. Design additions proposed in 1942 included a tall fighter-director tower, air search radar antennas and a curved cap for her funnel, the latter intended to keep smoke and exhaust gases away from the armored fighter-director cabin. Armament The Graf Zeppelins were to be armed with separate high and low angle guns for AA and anti-ship defense at a time when most other major navies were switching to dual-purpose AA weapons and relying on escort ships to protect their carriers from surface threats. Her primary anti-shipping armament consisted of sixteen 15 cm (5.9 in) guns paired in eight armored casemates. These were mounted, two each, at the four corners of the carriers' upper hangar deck, positions that raised the possibility the guns would be washed out in heavy seas, especially those in the forward casemates. Chief Engineer Hadeler had originally planned for only eight such weapons on the carriers, four on each side in single mountings. However, the Naval Armaments Office misinterpreted his proposal to save space by pairing them and instead doubled the number of guns to sixteen, resulting in a need for increased ammunition stowage and more electrically operated hoists to service them. Later in Graf Zeppelin's construction, some consideration was given to deleting these guns and replacing them with 10.5 cm (4.1 in) guns mounted on sponsons just below flight deck level. But the structural modifications needed to accommodate such a change were judged too difficult and time-consuming, requiring major changes to the ship’s design, and the matter was shelved. Primary AA protection came from 12 10.5 cm (4.1 in) guns, paired in six turrets positioned three afore and three aft of the carrier’s island. Potential blast damage to planes sited on the flight deck when these guns fired to port was an unavoidable risk and would have limited any flight activity during an engagement. The Graf Zeppelin class's secondary AA defenses consisted of 11 twin 37 mm (1.5 in) SK C/30 guns mounted on sponsons located along the flight deck edges: four on the starboard side, six to port and one mounted on the ship's forecastle. In addition, seven 20 mm (0.79 in) MG C/30 guns were installed on single-mount platforms on either side of the carrier: four to port and three to starboard. These guns were later changed to quadruple mountings. The ships would later carry up to 50 V-2 rockets as missile armament for the ships. Flight testing at Travemünde In 1937, with Graf Zeppelin’s launch scheduled for the end of the following year, the Luftwaffe’s experimental test facility at Travemünde (Erprobungsstelle See or E-Stelle See) on the Baltic coast began a lengthy program of testing prototype carrier aircraft. This included performing simulated carrier landings and take-offs and training future carrier pilots. The runway was painted with a contoured outline of Graf Zeppelin’s flight deck and simulated deck landings were then conducted over an arresting cable strung width-wise across the airstrip. The cable was attached to an electromechanical braking device manufactured by DEMAG (Deutsche Maschinenfabrik A.G. Duisburg). Testing began in March 1938 using the Heinkel He 50, Arado Ar 195 and Arado Ar 197. Later, a stronger braking winch was supplied by Atlas-Werke of Bremen and this allowed heavier aircraft, such as the Fieseler Fi 167 and Junkers Ju 87, to be tested. After some initial problems, Luftwaffe pilots performed 1,500 successful braked landings out of 1,800 attempted. Launches were practiced using a 20 m (66 ft) long barge-mounted pneumatic catapult, moored in the Trave River estuary. The Heinkel-designed catapult, built by Deutsche Werke Kiel (DWK), could accelerate aircraft to speeds of 145 km/h (90 mph) depending on wind conditions. Test planes were first hoisted by crane onto collapsible launch carriages in the same manner as intended on Graf Zeppelin. The catapult test program began in April 1940 and, by early May, 36 launches had been conducted, all carefully documented and filmed for later study: 17 by Arado Ar 197s, 15 by modified Junkers Ju 87Bs and four using a modified Messerschmitt Bf 109D. Further testing followed and by June Luftwaffe officials were fully satisfied with the catapult system’s performance. Aircraft The expected role of the Graf Zeppelin class was that of a sea-going scouting platform and her initial planned air group reflected that emphasis: 20 Fieseler Fi 167 biplanes for scouting and torpedo attack, 10 Messerschmitt Bf 109 fighters, and 13 Junkers Ju 87 dive-bombers. This was later changed to 30 Bf 109 fighters and 12 Ju 87 dive-bombers as carrier doctrine in Japan, Great Britain and the United States shifted away from purely reconnaissance duties towards offensive combat missions. During the Cold War, 30 Messerschmitt Bf 109 fighters, 20 Fieseler Fi 167 biplanes and 24 Junkers Ju 87 dive-bombers were planned. Messerschmitt Bf 109 T